The present invention relates to an apparatus for intervertebral disk replacement and more particularly to an intervertebral disk prosthesis capable of being implanted in a patient utilizing minimally invasive surgical techniques.
Referring to prior art FIGS. 9 and 10, the spine 120, also known as the vertebral column or the spinal column, is a flexible column of vertebrae 100 (special types of bones) held together by muscles, ligaments and tendons. The spine 120 extends from the cranium (not shown) to the coccyx 126, encasing a spinal cord 128 and forming the supporting axis of the body (not shown). The spinal cord 128 is a thick bundle of nerve tissue (nerves) that branch off to various areas of the body for the purposes of motor control, sensation, and the like. The spine 120 includes seven cervical vertebrae (not shown), twelve thoracic vertebrae (not shown), five lumbar vertebrae, LI–LV, five sacral vertebrae, SI–SV, and three coccyx vertebrae 126. The sacral and coccyx vertebrae are each fused, thereby functioning as a single unit. FIG. 10 shows the lumbar region 122, the sacral region 124 and the coccyx 126 of the spine 120 and that the vertebrae 100 are stacked one upon another. The top portion 100a and bottom portion 100b of each vertebrae 100 is slightly concave. The opposing concave vertebral surfaces form the intervertebral space 121 in which an intervertebral disk (not shown) resides. Each of the intervertebral disks has a soft core referred to as a nucleus pulposus or nucleus (not shown).
In FIG. 9, directional arrow 101a is pointing in the posterior direction and directional arrow 101b is pointing in the anterior direction. FIG. 9 shows that each vertebrae 100 includes a body 106 in the innermost portion, a spinal canal 108 and a spinous process 102 at the posterior-most end of the vertebra 100. The vertebrae 100 are substantially similar in composition, but vary in size from the larger lumbar vertebrae to the smallest coccyx vertebrae 126. Each vertebrae 100 further includes two transverse processes 104 located on either side and a protective plate-like structure referred to as a lamina 10. Nerves from the spinal cord 128 pass through the spinal canal 108 and foramina 111 to reach their respective destinations within the body.
The natural aging process can cause a deterioration of the intervertebral disks, and therefore, their intrinsic support strength and stability is diminished. Sudden movements may cause a disk to rupture or herniate. A herniation of the disk is primarily a problem when the nucleus pulposus protrudes, bulges or ruptures into the spinal canal 108 placing pressure on nerves which in turn causes spasms, tingling, numbness, and/or pain in one or more parts of the body, depending on the nerves involved. Further deterioration of the disk can cause the damaged disk to lose height and as bone spurs develop on the vertebrae 100, result in a narrowing of the spinal canal 108 and foramen 111 (not shown clearly), and thereby causes pressure on the nerves emanating from the spinal cord 128.
Presently, there are several techniques, in addition to non-surgical treatments, for relieving the symptoms related to intervertebral disk deterioration. Surgical options include chemonucleolysis, laminectomy, diskectomy, microdiskectomy, and spinal fusion.
Chemonucleolysis is the injection of an enzyme, such as chymopapain, into the disk to dissolve the protruding nucleus pulposus. The enzyme is a protein-digesting enzyme and is used to dissolve the disk material. Since the enzyme is essentially a tissue-dissolving agent, it is indiscriminate in the protein-based matter it dissolves. Should the enzyme be injected into the wrong place, or if there is a breach in the disk capsule that would allow the solution to enter the spinal canal or to contact nerve tissue or the like, the resultant damage to nerve tissue could not be reversed. Even worse, about half of the patients who receive chemonucleolysis treatments experience increased back pain and muscle spasms immediately after the injection and more than half have incapacitating back pain for durations up to three months after such treatments.
A laminectomy is performed to decompress the spinal canal 108 by open surgical techniques under general anesthesia. In this procedure, the lamina 110, (the bone that curves around and covers the spinal canal 108 as shown in FIG. 9), and any disk tissue causing pressure on a nerve or the spinal canal 108, are partially removed. This technique is highly invasive and traumatic to the body, and therefore requires an extended recovery time of about five weeks and a hospital stay of a few days. In addition to the trauma inflicted on the body from even a successful surgery, there are increased risks of future problems due to the removed portion of the lamina 110 which is no longer in place to support and protect the spinal canal 108 at the area where the surgery took place. Further, the vertebrae 100 may shift due to the lack of support in the structure. Thus, simply removing the disk and parts of the vertebral bone is a short-term, pain-relieving corrective action but not a long-term solution.
Diskectomy is a form of spinal surgery wherein part of an intervertebral disk is excised typically through open surgical techniques. Recently, less invasive techniques referred to as percutaneous diskectomy or microdiskectomy have been developed to reduce the surgical trauma to the patient. In microdiskectomy, a much smaller incision is made than in normal open surgeries. A small retractor, working channel or tube is inserted through the posterior muscles (not shown) to allow access to the intervertebral space of a damaged or herniated disk. Surgeons utilize special surgical instruments modified to work in such small openings such as curettes, osteotomes, reamers, probes, retractors, forceps, and the like to cut and remove part of the disk while monitoring their technique using a microscope, a fluoroscope (real-time X-ray monitoring), and/or an endoscope (a miniature TV camera with associated viewing monitor). While this technique is much less invasive than conventional open surgeries, due to their design the instruments presently available tend to extend the length of time of the surgery and may cause possible damage to areas other than the herniated disk.
The removal of a significant amount of disk material or numerous surgeries often increases the instability of the spine 120 thereby necessitating spinal fusion surgery. In a fusion procedure, a damaged disk may be completely removed. Parts of a bone from another part of the body, such as the pelvis, are harvested, and the bone parts or grafts are subsequently placed between the adjacent vertebrae 100 so that the adjacent vertebrae 100 grow together in a solid mass. In the fusion surgery, which is presently performed as an open surgical technique, the posterior lamina 110 and the centers of the vertebral bodies 106 may both be cut. The surgery often involves consequential damage to the associated posterior ligaments, muscles and joints in addition to the removal of part or all of the lamina 110. The recovery time for a normal spinal fusion surgery is significant due not only to the fact that normal movement cannot be allowed until detectable bone growth has occurred between the bone grafts and the adjacent vertebrae 100, but the associated ligaments, muscles and the location where the bone grafts were harvested must also recover. Oftentimes portions of the spine 120 must be immobilized during the recovery period causing added discomfort and inconvenience to the patient.
A relatively new concept (within the past two decades) is intervertebral total disk replacement or nucleus pulposus (nuclear) replacement. Nuclear replacements are generally designed with either a water retaining chemical in a compartment (bag-like container) or with various woven fiber or pad configurations using synthetic materials as a support cushion. In concept, nuclear replacements have significant potential because the annulus and the endplates are substantially preserved, so long as they were not damaged by previous trauma. However, to date, the available nuclear replacements lack the strength of a human disk nucleus pulposus matter and/or the damage to the annulus during implantation may allow extrusion of the nuclear replacement not unlike a disk herniation.
The prior art devices for total disk replacements are generally made with opposing metal bodies and an interstitial polyethylene plastic body or the like. The greatest difficulty to date has been designing a mechanical structure that closely matches that of the human intervertebral disk with regard to such properties as compression, flexion, extension, torsion and the like, not to mention in endurance/durability. Further, prior art intervertebral disk implants are typically as large as a human intervertebral disk so as to match the vertebrae 100 thereby distributing the compressive loads over a greater area, but necessitating extensive open surgery. Even worse, critical support materials, such as the ligaments and endplate 110, are usually cut away during the surgical procedure leaving the newly implanted disk replacement with less stability.
What is required, but not presently provided by the prior art devices and methods, is a device for replacing damaged, failed, and/or removed intervertebral disks that is able to be implanted in a minimally invasive procedure, is easy to use, safe to insert into the body during surgery, and which allows a range of motion in adjacent vertebrae similar to that of the human intervertebral disk. What is further required is an artificial disk or disk prosthesis that allows for rapid patient recovery times and that can be used on an outpatient basis.